Room-temperature cycling of metal fluoride electrodes: Liquid electrolytes for high-energy fluoride ion cells

VK Davis and CM Bates and K Omichi and BM Savoie and N Momcilovic and QM Xu and WJ Wolf and MA Webb and KJ Billings and NH Chou and S Alayoglu and RK McKenney and IM Darolles and NG Nair and A Hightower and D Rosenberg and M Ahmed and CJ Brooks and TF Miller and RH Grubbs and SC Jones, SCIENCE, 362, 1144-+ (2018).

DOI: 10.1126/science.aat7070

Fluoride ion batteries are potential "next-generation" electrochemical storage devices that offer high energy density. At present, such batteries are limited to operation at high temperatures because suitable fluoride ion-conducting electrolytes are known only in the solid state. We report a liquid fluoride ion-conducting electrolyte with high ionic conductivity, wide operating voltage, and robust chemical stability based on dry tetraalkylammonium fluoride salts in ether solvents. Pairing this liquid electrolyte with a copper-lanthanum trifluoride (Cu@LaF3) core-shell cathode, we demonstrate reversible fluorination and defluorination reactions in a fluoride ion electrochemical cell cycled at room temperature. Fluoride ion-mediated electrochemistry offers a pathway toward developing capacities beyond that of lithium ion technology.

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